This application claims the benefit of International Application Number PCT/EP00/00942, which was published in English on Sep. 14, 2000.
The present invention refers to an improved apparatus for maintaining a prefixed orientation when conveying on a large-scale basis orderly sequences of containers made of thermoplastic material, in particular polyethylene terephtalate (PET) and polypropylene (PP), in particular appropriate semi-finished items generally known as xe2x80x9cpreformsxe2x80x9d in the art, which are usually blow-moulded subsequently for conversion into finished containers.
In particular, the present invention can be used in a most advantageous manner when the described apparatus, which in the following description will be referred to as a xe2x80x9cpick-up plugxe2x80x9d after the name under which it is widely known by those skilled in the art, is associated to a preform production plant that is also known in the art as a single-stage plant, but can of course be advantageously used also in connection with plants that are solely fed with previously produced preforms to only carry out the final blow-moulding phase (two-stage plants).
As a matter of fact, these processes for the production of such types of containers are generally known to be able to be schematically divided into two basic typologies, ie. single-stage and two-stage processes.
In two-stage processes, a previously moulded preform or parison in a substantially amorphous state is heated up again to its preferred molecular orientation temperature, at which it is then blow-moulded to the desired shape. As used this particular context, the term xe2x80x9ctwo-stage processxe2x80x9d, or simply xe2x80x9ctwo-stagexe2x80x9d, is intended to mean any process that produces a preform or parison which must subsequently be heated up again from ambient temperature to the respective blow-moulding temperature.
On the contrary, single-stage processes are so defined owing to the fact that they are capable of moulding said so-called preform or parison, transferring the same preform or parison from the injection or extrusion mould (after it has cooled down to some appropriate temperature) to a conditioning station, where said preform or parison is allowed to evenly balance down to a preferred molecular orientation temperature. Said preform or parison is then transferred to a blow-moulding tool, where it is moulded into the desired shape.
The state of the art concerning the techniques used to solve the problems connected with the injection moulding and extrusion of said preforms, the final blow-moulding thereof, as well as the synchronization of the related processes in view of increasing the efficiency and productivity of the plant, is exhaustively described in the European patent application EP 0 768 165, filed by this same Applicant, which also describes the most significant patents covering this matter, and to which reference should therefore be made.
Both above cited types of production methods involve the use of a (per sxc3xa9 known) blow-moulding station and the therewith associated handling means for transferring and releasing the preforms and/or the blow-moulded containers after the blow-moulding phase.
Largely known in the art are also the problems connected with the transfer, or conveyance, of the preforms. The system used to transport these preforms from the injection-moulding station through to the final container ejection station, via the conditioning and blow-moulding stages, is namely based, in the current single-stage blow-moulding plants by SIPA, on the use of said pick-up plugs.
These pick-up plugs are capable of supporting and carrying the preforms, allowing them to be rotated in those cases in which a conditioning process by hot air is used.
In this case, in fact, the pick-up plug is constituted by a xe2x80x9cstatorxe2x80x9d, which is appropriately coupled to the driving belt, and a rotor (or collar body), which is free to rotate about its axis and which is driven rotatably in the conditioning station for as long a time as necessary for the hot air to be able to heat up the preform supported by it.
This capability of rotating freely does not however enable the preform or the container to be known to be in a given, pre-established position at any given time, and sometimes this may be a problem, actually.
In particular, this occurs when
1) a well-defined orientation of the thread (which is obtained by injection moulding) with respect to some match or reference on the container (which is obtained by blow moulding) is required;
2) diametrically asymmetrical preforms are used, which are required to enter the blow-moulding tool with a well-defined orientation, wherein this orientation is usually lost during the conditioning phase;
3) diametrically asymmetrical (ovally shaped bottles for detergents), squared containers are produced or in the case in which a particular orientation is required downstream of the blow-moulding tool owing to the need for a matching interface to be created between the latter and the container ejection and unloading system, which is provided with appropriate collection cups that are given a similar shape as the containers they are intended to accommodate.
The fact should also be mentioned at this point that the container undergoes a rotation when the blow-moulding tool is opened, owing to the friction occurring between the die and the same container.
The above cited problems, along with further ones arising when a given orientation of the preform or container is required, can be solved by the use of a pick-up plug whose orientation is capable of being pre-established and ensured each time that it is left in a resting position.
U.S. Pat. No. 5,282,526 discloses a device for holding container preforms on carriers for further processing. A preform is put onto the rotatable part of a carrier at an indefinite angular position thereof. Subsequent reorientation is therefore necessary.
Based on the above considerations, it is therefore a main purpose of the present invention to provide a pick-up plug that makes use of permanent magnets which are appropriately arranged and fixed on the stator and rotor thereof so as to allow for, when at rest, a multiplicity of different orientations, such as the one required in the conditioning station.
It is a further purpose of the present invention to provide a pick-up plug of the above cited kind, which is additionally capable of feeding in a substantially continuous and automatic manner the connected processing plants, without any interposition of non-automatic phases or phases that may break the continuity of the feeding flow of preforms or blow-moulded containers; moreover, such a pick-up plug must be easily implemented with the use of readily available techniques and means and shall therefore be reasonably low in its overall costs.
Such main aims of the present invention, along with further features thereof, are reached in an apparatus that is made and operates as recited in the appended claims.